1. Field of the Invention
The present invention relates to an ink composition suitable for use in image recording in which ink is ejected by an ink-jet method. The invention also relates to an ink set and an ink-jet recording method using the ink composition.
2. Description of the Related Art
Ink-jet recording methods use a large number of nozzles arranged in an ink-jet head, from which ink droplets are ejected when recording is performed. Ink-jet recording methods are widely used, because they make it possible to record high-quality images on a variety of recording media.
Known ink-jet recording methods include two-liquid reaction type recoding methods in which two liquids: ink and a treating liquid for aggregating the ink are allowed to react with each other so that the ink is aggregated, which facilitates fixing of the ink. For example, a known ink-jet recording method includes depositing, on a recording medium, an ink composition containing a pigment and a resin emulsion and a reactive liquid containing a polyvalent metal salt. It is considered that according to this method, image blurring or image unevenness can be reduced (see for example Japanese Patent Application Laid-Open (JP-A) No. 07-32721).
On the other hand, when recording is performed on plain paper or the like, sufficient performance sometimes cannot be obtained with respect to, for example, fixing property (for example, scratch resistance) or resolution, in addition to color forming density. In particular, this is the case when increasing the speed of ink-jet recording, and a recording method more suitable for high speed recording using a single pass system capable of recording by one operation of a head, as opposed to a shuttle scanning system, is in demand.
After the recording, a sheet of paper or the like is placed on the recorded image in various cases such as collection and storage. If sticking, adhesion, or the like occurs between the image portion and a sheet of paper or the like placed thereon, various problems such as damage to the image and degradation of handleability may occur. In order to obtain images free from sticking and so on, methods of increasing the filming temperature or Tg (glass transition temperature) of the resin component of the ink may be used. However, if Tg or the like is raised, the temperature necessary for heat treatment to achieve fixing performance such as scratch resistance will be raised, which increases the thermal energy consumption for the fixing.
In this regard, a specific ink-jet recording method is disclosed, which includes the steps of providing an ink composition containing a resin emulsion having a minimum filming temperature of 50° C. or more, writing an ink image with the ink composition on a transfer medium whose surface is heated to a temperature equal to or higher than the minimum filming temperature of the resin emulsion, evaporating the solvent component of the ink image on the transfer medium, and transferring the ink image from the transfer medium to a recording medium (see for example JP-A No. 07-32721).
It has been found that when the ink composition used is prepared such that the Minimum Filming Temperature (hereinafter also abbreviated as “MFT”) of polymer particles in the ink composition can be kept at a relatively low level at the image recording stage and such that after the recording, the MFT can be changed to a relatively high level over time or by heating for drying or the like, both anti-blocking property and scratch resistance can be imparted to image portions, while thermal energy can be saved. The invention has been made based on the finding.